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Highly Sensitive Molecular Assay for Group A Streptococci Over-identifies Carriers and May Impact Outpatient
Robert R Tanz1,2, Elizabeth J Ranniger2,3, Jason L Rippe4
1From the Division of Academic General Pediatrics, Ann & Robert H. Lurie Children's Hospital of Chicago.
Background:
Timely, accurate diagnosis of group A streptococci (GAS) pharyngitis prevents acute rheumatic fever and limits antibiotic overuse. The illumigene group A Streptococcus assay (Meridian Bioscience, Cincinnati, OH) is a molecular test for GAS pharyngitis with high sensitivity and specificity. We sought to determine whether the illumigene test is more likely than throat culture to be positive in patients without pharyngeal symptoms and explore the limits of detection of the test.
Methods:
Patients 3-17 years of age were eligible if they had no history of pharyngitis or use of antibiotics within the previous 2 weeks; there were no upper respiratory infection symptoms, sore throat or fever and no signs of infection. Culture and illumigene were performed on duplicate throat swabs. Excess lysate from a subset of illumigene tests was evaluated by real-time polymerase chain reaction. Institutional Review Board approval was obtained.
Results:
We enrolled 385 patients from February 2016 to October 2017; mean age was 10 yr; 51% were male. Most visits were for health supervision (69%). Significantly more illumigene tests (78/385, 20.3%) than throat cultures (48/385, 12.5%) were positive (χ; P =0.0035). Illumigene was "indeterminate" for 3 patients, leaving 382 pairs of swabs for analysis. Results were discordant for 32 of 382 pairs (8.4%); 31 of 32 (97%) were illumigene-positive/culture-negative (McNemar test; P < 0.000001). Real-time polymerase chain reaction was negative in 4 of 13 (31%) tested illumigene-positive lysates; the paired culture had been negative in all four. The limit of detection for the illumigene test was 55 colony forming units/mL.
Conclusions:
The illumigene test is significantly more likely than throat culture to yield positive results in patients without GAS pharyngitis. Failure to appropriately select patients for testing may negatively impact antimicrobial stewardship efforts without benefit to patients.
Insights
The illumigene group A Streptococcus assay is more likely to return positive results than throat cultures in patients without pharyngitis symptoms. This finding suggests potential overuse of antibiotics and impacts antimicrobial stewardship efforts.
Area of Science:
- Clinical microbiology
- Infectious disease diagnostics
- Molecular diagnostics
Background:
- Accurate diagnosis of group A streptococci (GAS) pharyngitis is crucial for preventing acute rheumatic fever and limiting antibiotic overuse.
- The illumigene group A Streptococcus assay is a molecular diagnostic tool for GAS pharyngitis, known for its high sensitivity and specificity.
Purpose of the Study:
- To compare the positivity rates of the illumigene test versus throat culture in patients presenting without pharyngeal symptoms.
- To investigate the limit of detection for the illumigene test in identifying GAS.
Main Methods:
- A study involving 385 patients aged 3-17 years with no prior history of pharyngitis or recent antibiotic use.
- Duplicate throat swabs were collected for both illumigene testing and throat culture.
- Real-time polymerase chain reaction (PCR) was used to evaluate excess lysate from a subset of illumigene tests.
Main Results:
- The illumigene test yielded significantly more positive results (20.3%) compared to throat culture (12.5%) in the study population.
- Discordant results were observed in 8.4% of cases, with 97% of these being illumigene-positive and culture-negative.
- The limit of detection for the illumigene test was determined to be 55 colony-forming units/mL.
Conclusions:
- The illumigene test demonstrates a higher likelihood of positive results compared to throat culture, particularly in patients without GAS pharyngitis symptoms.
- Inappropriate patient selection for illumigene testing may lead to overestimated infection rates, potentially impacting antimicrobial stewardship without clinical benefit.
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